In general, this invention relates to an apparatus for use in producing magnetic recording media. In particular, it relates to an improved apparatus for orienting the magnetic particles used in the manufacturing of such media.
Several techniques are known for producing magnetic recording media. Typically, they include applying a magnetic coating containing tiny magnetic particles uniformly dispersed in a curable binder on a tape or disk surface. For giving the particles a preferred directional orientation they are passed through a magnetic orienting field. This is done so that their axes of easy magnetization align with the flux of the field. Use of magnetic recording media is determined typically by the orientation of the magnetic particles. For permanently setting these particles in a desired orientation, the coating is cured or dried.
The most common orientation for such particles is to have their axes of easy magnetization arranged in end-to-end fashion along the longitudinal extent of, for example, a tape. This is usually achieved by a pair of spaced-apart permanent bar-type magnets having poles of the same polarity facing each other and passing the magnetic layer between the oppositely facing poles.
Examples of known techniques for achieving the foregoing kind of orientation are illustrated and described in the following U.S. Pat. Nos.: 2,711,901; 3,117,065; 3,437,514 and 3,775,178.
For purposes of enhancing the density packing of particles, so as to improve recording characteristics of recording media, it has been proposed to orient these particles so that their axes of easy magnetization are generally perpendicular with respect to the tape surface. By having them generally perpendicular, there is greater concentration of particles per unit area having the desired orientation. Accordingly, more electronic information can be stored.
Previously referenced U.S. Pat. No. 2,711,401 also illustrates and describes a process, whereby the magnetic particles are oriented generally perpendicularly. This is achieved under the influence of a magnetic field created by permanent magnets spaced apart and having magnetically opposing poles facing each other. As the particles pass through this field in an uncured binder, they tend to rotate so that their easy axes align with the flux lines of such fields. Subsequently, the binder is cured for permanently setting the particles in this preferred orientation. However, upon leaving the field, the still uncured particles tend to assume a generally horizontal orientation.
The foregoing described patents use unprotected bar-type permanent magnets for orienting the particles. For generating sufficiently strong fields for orienting purposes, these magnets tend to be relatively large. Recently, it has been proposed to use stronger rare earth magnets for effecting such orientation. U.S. Pat. No. 4,338,643 describes an approach using high coercivity magnets, such as samarium cobalt for orienting the magnetic particles. In general, however, use of high coercivity magnets, presents problems because they tend to be relatively expensive and relatively small in size. Also, these magnets are relatively difficult to handle due to their strong fields. Hence, their assembly in closely packed and stable relationship, whereby all magnets are in juxtaposed relationship with the poles facing in a common direction is often difficult due to the repulusive and attractive forces. Known orienting magnets in this field tend to be physically unprotected. This is a significant drawback when manufacturing magnetic recording media, since there is a possibility that their effectiveness is diminished by uncured coating material contacting them.